1. Field of the Invention
The present invention relates to an optical information recording medium for recording/reproducing information at high speed and high density using optical means such as a laser beam.
2. Description of the Related Art
A technique of recording/reproducing information at high density using a laser beam is known. Mainly, optical disks have been put into practical use for such a purpose.
Optical disks are classified roughly into a read-only type, a write-once type, and a rewritable type. Examples of the read-only type include compact disks and laser disks. The write-once type and the rewritable type are used for document files, data files, etc. The rewritable optical disks are classified mainly into a magneto-optical type and a phase-change type. The phase-change type optical disks use a reversible change in a recording layer between an amorphous phase and a crystalline phase (or between different crystal structures) under the irradiation with a laser beam. In this case, recording is performed by changing at least one of a refractive index or an extinction coefficient of a thin film under the irradiation with a laser beam, and the amplitude of transmission light or reflection light is changed in an area irradiated with a laser beam. Therefore, in general, the phase-change type optical disk includes a dielectric layer, a recording layer, a reflection layer, and a protection layer on a substrate. There is an example of a disk structure in which a first dielectric layer, a recording layer, a second dielectric layer, a reflection layer, and a protection layer are formed on a substrate in this order.
For the dielectric layer, compounds such as SiO2, SiO, TiO2, MgO, Ta2O5, Al2O3, GeO2, SiC, ZnS, ZnSe, ZnTe, and PbS, those mainly containing a nitride, such as Ge3N4, Si3N4, SbN, BN, and AIN, or mixtures thereof can be used.
Furthermore, JP 09-834298 A and JP 10-275360 A disclose optical disks with enhanced cycle characteristics, in which a GeON dielectric layer or a GeN dielectric layer is provided between the above-mentioned dielectric layer and the recording layer.
Examples of the material for the substrate include glass, quartz, polycarbonate, and polymethylmetahcrylate. Furthermore, the substrate may be made of a smooth flat plate, or may have groove-shaped unevenness for tracking. A signal is reproduced in this unevenness by detecting a change in amount of transmission light or reflection light that leads to an information recording/reproduction detection system. When seen from an incident side of a laser beam for reproduction, a distant portion (i.e., a convex portion on a disk substrate) is called a land, and a close portion (i.e., a concave portion on a disk substrate) is called a groove.
The protection layer can be obtained by dissolving resin in a solvent, followed by coating and drying, or by attaching a resin plate with an adhesive.
The recording layer, dielectric layer, and reflection layer are formed on a transparent substrate by vacuum deposition or sputtering.
High reliability is required of optical disks, such as high density recording, large capacity, and repeated recording/reproduction characteristics (hereinafter, referred to as xe2x80x9ccycle characteristicsxe2x80x9d). In order to record information on an optical disk at high density, for example, small recording marks are formed by using a laser beam with a short wavelength, and the widths of the groove and the land on a substrate are required to be small. Recording information on both a land and a groove (land and groove recording) also is advantageous for high-density recording.
However, it is difficult to keep reliability such as cycle characteristics while performing high-density recording. In particular, when land and groove recording is performed on a phase-change type optical disk, cycle characteristics are likely to be degraded in the land along with an increase in the number of recording/reproduction.
When recording is repeated a number of times, a jitter value is increased, which is caused by local movement of a material in the recording layer. When a signal is recorded on a phase-change type optical disk, the recording layer is headed to about 600xc2x0 C. with a laser beam, followed by melting and cooling. Repeated recording of a signal results in the repetition of this cycle; consequently, other layers forming a disk such as a dielectric layer and a disk substrate are subjected to thermal expansion and contraction repeatedly. Thus, it is conceivable that the local movement of a material in the recording layer is caused by the expansion and contraction. The reason for the difference in cycle characteristics between the land and the groove is not known. Although an exact mechanism is not known, the following is supposed: the heated recording layer is cooled differently between the land and the groove; the land is less likely to be cooled, so that the land may reach a temperature higher than that of the groove; the land is just less likely to be cooled and returns to a room temperature finally; therefore, the land is subjected to a larger temperature difference, resulting in larger expansion and contraction, compared with the groove.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an optical information recording medium with satisfactory cycle characteristics, in which movement of a material in a recording layer is suppressed even when so-called land and groove recording is performed repeatedly.
In order to achieve the above-mentioned object, the first optical information recording medium of the present invention is a phase-change type optical disk including, on a transparent substrate having a convex land and a concave groove for tracking, a phase-change type recording layer in which an optically detectable reversible change occurs between an amorphous phase and a crystalline phase at least by irradiation with an energy beam,
wherein a signal is recorded on both the land and the groove, the phase-change type optical disk includes a dielectric layer in contact with at least one side of the phase-change type recording layer, the phase-change type recording layer contains, as its main component, at least one selected from the group consisting of Te, Se, Sb, In, Ge, and Ag,
the dielectric layers contain, as main components thereof, at least one selected from the group consisting of Ge and Si, and N, and contain an element xcex2 (where xcex2 is at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Cu, Ag, Au, Zn, and Cd), and
the phase-change type recording layer contains an element xcex1 (where xcex1 is at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Cu, Ag, Au, Zn, and Cd).
The second optical information recording medium of the present invention includes, on a transparent substrate having unevenness for tracking, a phase-change type recording layer that reversibly changes between an amorphous phase and a crystalline phase and contains at least one selected from the group consisting of Te, Se, Sb, and In, wherein a thickness of then phase-change type recording layer is in a range of 5 nm to 15 nm, a dielectric layer containing at least one selected from the group consisting of Ge and Si, and N are formed so as to be in contact with the phase-change type recording layer, and the dielectric layer contains an element xcex3 (where xcex3 is at least one element selected from the group consisting of Sb, Te, Se, Sn, Ga, and In).